Spinal implant connection assembly

ABSTRACT

A variable angle connection between a spinal rod (A) and a vertebral anchor (B) with a clevis ( 3 ) to attach to the vertebral anchor, permitting the vertebral anchor to be longitudinally offset from the connecting point on the rod. The connection assembly has a bolt ( 2 ) with an aperture ( 6 ) for receiving a portion of the spinal implant rod at one end. The assembly also has a clevis ( 3 ). The clevis defines a bore ( 7 ) to hold a portion of the vertebral anchor and the ears ( 8, 9 ) of the clevis have holes through which the bolt is located with the bolt rotatably connected to the ears. The assembly also has a rod interface washer ( 4 ) positioned over a portion of the bolt, between the aperture ( 6 ) of the bolt and the inside ear of the clevis. The rod interface washer is partly movable between the aperture of the bolt and the clevis, but the washer is fixed against rotating in relation to the bolt. Finally, the assembly also includes a compression member ( 5 ) that pushes the rod toward the vertebral anchor so that the inside and outside ears of said clevis are pressed together and the clevis is tightened the vertebral anchor.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of provisionalpatent application Serial No. 60/466,148, filed Apr. 28, 2003, which isincorporated herein by reference. This application is acontinuation-in-part of U.S. patent application Ser. No. 09/694,291,filed Oct. 23, 2000, which is a continuation-in-part application ofApplicant's U.S. patent application Ser. No. 09/526,104, filed Mar. 15,2000, both of which are incorporated herein by reference. These claimsfor priority are neither admissions nor indications by the Applicant orinventor that the claimed inventions are not entirely supported by theprior application.

FIELD OF THE INVENTION

[0002] This invention relates to a spinal implant connection between aspinal rod and a vertebral anchor, and more particularly relates to aspinal implant connection with a clevis to attach to the vertebralanchor.

BACKGROUND

[0003] Spinal implant systems provide a rod for supporting the spine andfor properly positioning components of the spine for various treatmentpurposes. Bolts, screws, and hooks are typically secured to thevertebrae for connection to the supporting rod. These vertebral anchorsmust frequently be positioned at various angles due the anatomicalstructure of the patient, the physiological problem being treated, andthe preference of the physician. It is difficult to provide secureconnections between the spinal support rod and these vertebral anchorsat all the various angles that are required, especially where there aredifferent distances between the rod and bolts and where these componentsare located at different heights on the patient.

[0004] One solution to this problem is shown in U.S. Pat. Nos. 5,643,263and 5,885,285 to Simonson, the disclosures of which are specificallyincorporated into this specification by reference. These patentsdescribe a connection between a rod and a vertebral anchor, throughwhich a surgeon may vary the angle between a spinal rod and the anchorto which the rod is attached. The connection is equipped with aninterlocking set of washers that allow the surgeon to fix the desiredangle between the anchor and the rod. In general, this system requiresthe surgeon in a typical installation to either sacrifice the capsule ofthe facet joint that may reside next to the connection, or elevate theconnection above the facet joint and thereby raise the profile of theentire spinal implant system at that location. Occasionally, however,the surgeon may not wish to exercise either of these options in aparticular surgery. Hence, an improvement over the device shown in theseearlier patents would be a connection assembly that simultaneouslyminimizes the profile of the spinal implant system above the patient'sspine without generally requiring the surgeon to sacrifice a facet jointthat may reside next to a particular rod-to-vertebral-anchor connectionassembly. The following invention is one solution to that need.

SUMMARY OF THE INVENTION

[0005] In one aspect, this invention is a connection assembly between aspinal implant rod and a vertebral anchor. The assembly has a bolt withan aperture for receiving a portion of the spinal implant rod at oneend. The assembly also has a clevis. The clevis defines a bore to hold aportion of the vertebral anchor and the ears of the clevis have holesthrough which the bolt is located with the bolt rotably connected to theears. The assembly also has a rod interface washer positioned over aportion of the bolt, between the aperture of the bolt and the inside earof the clevis. The rod interface washer is partly movable between theaperture of the bolt and the clevis, but the washer is fixed againstrotating in relation to the bolt. Finally, the assembly also includes acompression member, such as a screw, that forceably engages or threadsinto the side of the bolt and continues into the aperture of the bolt.The screw is used to push the rod toward the vertebral anchor so thatthe inside and outside ears of the clevis are pressed together and theclevis is tightened around the vertebral anchor.

[0006] Optionally, the inside ear of the clevis and the rod interfacewasher have mating male protrusions and female cavities on theirsurfaces such that, when pressed together, the protrusions and cavitiesengage to further prevent rotation of the clevis in relation to the rodinterface washer. In this alternative design, the protrusions andcavities have multiple interlocking orientations so that the rodinterface washer and the clevis can be interlocked in a plurality offixed angles in relation to each other.

[0007] An object of this invention is to reduce the physical mass thatis typically required to attach a spinal rod to a vertebral anchor.

[0008] An advantage of this invention is that the clevis allows avertebral anchor to be placed closer to the spinal rod than prior artdesigns that also use a single means to allow the surgeon to secure boththe anchor and the rod to the connection assembly in one tighteningstep.

[0009] A feature of this invention is that it allows the surgeon theoption of lowering the profile of a spinal attachment system closer tothe spine without requiring the surgeon to sacrifice the capsule of afacet joint that may reside next to the connection assembly. In otherwords, this invention allows the connection assembly to be placed in aposition that is medial to the facet joint.

[0010] As used in this specification the term “clevis” is used in itsordinary and accustomed meaning that being—“(1): a fitting for attachingor suspending parts (as a cable to another structural member of a bridgeor a hanger for supporting pipe) that consists usu. of a U-shaped pieceof metal with the ends drilled to receive a pin or bolt (2): any ofvarious connections in which one part is fitted between the forked endsof another and fastened by means of a bolt or pin passing through theforked ends.” Webster's Third New International Dictionary, Unabridged.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of a connection assembly constructedpursuant to this invention.

[0012]FIGS. 2 and 2A are end views of a connection assembly constructedpursuant to this invention.

[0013]FIGS. 3 and 3A are top views of a connection assembly constructedpursuant to this invention.

[0014]FIG. 4 is a top view of a bolt constructed pursuant to thisinvention.

[0015]FIG. 5 is a side view of a bolt constructed pursuant to thisinvention.

[0016]FIG. 6 is an end view of a bolt constructed pursuant to thisinvention.

[0017]FIG. 7 is a cross-sectional view of a bolt constructed pursuant tothis invention.

[0018]FIGS. 8 & 9 respectfully depict a stop in plan and elevationalviews constructed pursuant to this invention.

[0019]FIG. 10 is a cross-sectional view of clevis constructed pursuantto this invention.

[0020]FIG. 11 is an end view of a clevis constructed pursuant to thisinvention.

[0021]FIG. 12 is a side view of a clevis constructed pursuant to thisinvention.

[0022]FIG. 13 is a side view of one alternative embodiment of a clevisconstructed pursuant to this invention.

[0023]FIG. 14 is a side view of a second alternative embodiment of aclevis constructed pursuant to this invention.

[0024]FIGS. 15, 16 & 17 are respectively top, side, and cross-sectionalviews of a connection assembly constructed pursuant to this invention.

[0025]FIGS. 18, 19 & 20 are respectively end, side, and top views of arod interface washer constructed pursuant to this invention.

[0026]FIGS. 21, 22 & 23 are respectively top, side, and cross-sectionalviews of an embodiment of this invention.

[0027]FIGS. 24, 25 & 26 are respectively side, cross-sectional, and topviews of a bolt used in one embodiment of this invention.

[0028]FIGS. 27, 28 & 29 are respectively cross-sectional, side, andfront views of a clevis used in one embodiment of this invention.

[0029]FIG. 30 is a cross-sectional view of a clevis used in oneembodiment of this invention.

[0030]FIGS. 31, 32 & 33 are respectively front, a side and a second sideviews of one embodiment of a rod interface washer used in one embodimentof this invention.

[0031]FIG. 34 is a top plan view of a connection assembly according toanother embodiment of the present invention.

[0032]FIG. 35 is a view of the apparatus of FIG. 34 as taken along lines35-35 of FIG. 34.

[0033]FIG. 36 is a cross sectional view of the apparatus of FIG. 34 astaken along line 36-36 of FIG. 34.

[0034]FIG. 37 is a side elevational view of a bolt according to anotherembodiment of the present invention.

[0035]FIG. 38 is a view of the apparatus of FIG. 37 as taken along line38-38 of FIG. 37.

[0036]FIG. 39 is a cross sectional view of the apparatus of FIG. 38 astaken along line 39-39 of FIG. 38.

[0037]FIG. 40 is a side elevational view of a clevis according toanother embodiment of the present invention.

[0038]FIG. 41 is a view of the apparatus of FIG. 40 as taken along line41-41 of FIG. 40.

[0039]FIG. 42 is a cross sectional view of the apparatus of FIG. 41 astaken along line 42-42 of FIG. 41.

[0040]FIG. 43 is a front elevational view of a rod interface washeraccording to another embodiment of the present invention.

[0041]FIG. 44 is a view of the apparatus of FIG. 43 as taken along line44-44 of FIG. 43, with the view being rotated.

[0042]FIG. 45 is a view of the apparatus of FIG. 43 as taken along line45-45 of FIG. 43, with the view being rotated.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0043] Specific language is used in the following description topublicly disclose the invention and to convey its principles to others.No limits on the breadth of the patent rights based simply on usingspecific language are intended. Also included are any alterations andmodifications to the description that should normally occur to one ofaverage skill in this technology.

[0044] A connection assembly 1 according to the invention is shown inFIGS. 1-3. Connection assembly 1 is shown attaching a spinal implant rod“A” with a longitudinal axis L1 to the shaft of a vertebral anchor “B”with the longitudinal axis L2. Connection assembly 1 includes a bolt 2,a clevis 3, a rod interface washer 4, and a set screw 5. Bolt 2 has anaperture 6 for receiving a rod in a spinal implant system. While aclosed aperture is shown, it will nevertheless be understood that anopen-sided aperture may also be used to permit top-loading of theconnector rod. Set screw 5 is forceably inserted through a threadedopening 15 in bolt 5 and into aperture 6 so as to allow set screw 5 topush against rod A. Clevis 3 has a bore 7 for receiving a vertebralanchor in a spinal implant system. Clevis 3 wraps around the shaft ofvertebral anchor B and is simultaneously tightened when set screw 5 istightened against rod A. It is contemplated that the shaft of B may beroughened and the interior of clevis 3 may be correspondingly roughenedto increase friction between them. As set screw 5 pushes against rod A,rod A pushes against rod interface washer 4. This force pinches the ends8 and 9 of clevis 3 together between rod interface washer 4 and stop 10,which tightens clevis 3 around vertebral anchor B. In this manner, setscrew 5 acts as a compression member to tighten the connection assemblyand achieve substantial fixation.

[0045] Details of bolt 2 are shown in FIGS. 4-7. Bolt 2 can besubdivided into bolt head portion 11, bolt shaft portion 12, washer seatportion 13 and washer stop portion 14. Threaded openings 15 a & 15 b,and aperture 6 reside in bolt head portion 11. Threaded openings 15 a &15 b open into aperture 6 at an oblique angle A4 with respect tolongitudinal axis L3 to allow set screw 5 (FIGS. 1-3) to force spinalrod A toward the distal end 16 of aperture 6. Bolt 2 is substantiallysymmetrical about longitudinal axis L3 such that threaded openings 15 aand 15 b are substantially mirror images. Bolt shaft portion 12 isgenerally cylindrical in shape and is sized to accept the eyes (items 17and 18, FIG. 10) of clevis 3. Clevis 3 is then held on shaft portion 12by attaching stop 10 (shown in isolation in FIGS. 8 & 9) to the end 19of shaft portion 12, either by welding or some other suitable means. Asan alternative, shaft portion 12 may include threads and stop 10 may becorrespondingly threaded to be held in position. In this alternativedesign, stop 10 may be the compressive member utilized to tightenconnection assembly 1.

[0046] Bolt 2 also preferably includes washer seat portion 13 and washerstop portion 14. A seat portion 13 that is substantially rectangular incross-section is currently preferred, but washer seat portion 13 can beof any suitable shape that may interlock with a complementary shape inrod interface washer 4 (FIGS. 1-3) to prevent rod interface washer 4from rotating in relation to bolt 2. As shown, washer stop 14 isgenerally provided by placing a raised edge in bolt head portion 11.Washer stop 14 prevents rod interface washer 4 from being inadvertentlyremoved from connector assembly 1 during installation.

[0047] Referring to FIGS. 2A and 3A, additional characteristics of thepreferred embodiment may be seen by contrasting several of connectorassembly 1's relative dimensions. Dimension D1 is the overall width ofconnection assembly 1, measured from the most medial point 50 ofconnector assembly 1 to its most lateral point 51. Dimension D2 is thedistance from the inside edge of rod A to the outside edge of vertebralanchor B, measured perpendicularly to L1. Dimension D3 is the distancefrom the inside edge of rod A to the most lateral end 52 of bolt 2,measured perpendicularly to L1. Dimension D4 is the distance from theinside edge of rod A to the inside edge of vertebral anchor B, measuredperpendicularly to L1. Dimension D5 is the distance from the outsideedge of vertebral anchor B to the most lateral point 51 of connectorassembly 1. And dimension D6 is the distance from L2 to L3, measuredparallel to L1.

[0048] Contrasting several of these dimensions, most notably D3 can beless than D2 in the present invention. In other words the outside edge52 of bolt 2 does not need to extend beyond the outside edge ofvertebral anchor B. Typically, most connectors place the bore to hold avertebral anchor at the end of a bolt that typically holds the vertebralanchor to the rod, necessarily leaving a portion of the bolt extendingpast the vertebral anchor. An example of such a design is shown in U.S.Pat. Nos. 5,643,263 and 5,885,285 to Simonson. But here, bolt 2 does notneed to extend beyond anchor B, which would allow bolt 2 of connection 1to be placed in more narrow passageways than connections of prior artdesigns.

[0049] Next it should be noted that the present invention allowsdimension D4 to be shortened as the surgeon may desire, reducing theoverall width D1 of the connector assembly. In other words and referringalso to FIGS. 13 & 14, the present design allows D4 to be shortened byplacing the bore 7 of clevis 3 in a position that is closer to rod A.For example, clevis 3 shown in FIG. 14 could conceivably place vertebralanchor B so close to rod A that only the width of clevis 3 around bore 7would separate vertebral anchor B from rod A.

[0050] Finally, the present design also allows vertebral anchor B to belaterally offset a distance D6 from the longitudinal axis L3 of bolt 2,allowing bolt 2 and its connection to rod A to lie in a differenttransverse plane on the patient than vertebral anchor B would lie. Mostdesigns such as U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson placethe bore to hold vertebral anchor B in the same transverse plane as theconnection to rod A. In other words, vertebral anchor B is usuallysituated in line with the longitudinal axis of the structure, usually abolt, that holds the vertebral anchor B and rod A together. Here,however, the present invention allows bolt 2 to be placed in onetransverse plane (in one longitudinal location along rod A) andvertebral anchor B to be placed in another transverse plane (or anotherlongitudinal location along rod A). Thusly situated, bolt 2 is separatedfrom vertebral anchor B by a distance D6, measured longitudinally alongrod A. Moreover, D6 can be larger than D4, readily allowing bolt 2 to beplaced in one longitudinal position on the spine and vertebral anchor Bto be placed in another position, above or below bolt 2. Located in thisfashion, the surgeon can place the connector assembly of the presentinvention in a location that avoids interfering with the facet joints ofthe patient's spine.

[0051] Details of clevis 3 are shown in FIGS. 10-12. Clevis 3 includes abore 7, a proximal ear 8 or end 8 and a distal ear 9 or end 9. Proximalear 8 has an eye 18 and distal ear 9 has an eye 17. As previouslypresented, bolt 5 attaches to clevis 3 by placing the shaft portion ofbolt 5 through eyes 17 and 18 and then attaching end 10 (FIG. 15). Theproximal ear 8 also includes a connection surface 20. Connection surface20 preferably includes structure for facilitating the engagement ofclevis 3 against rotational movement relative to rod interface washer 4.This engagement structure is preferably a plurality of variable angleridges 21 that radiate from the rotational center of clevis 3. In otherwords, the structure is a set of interlocking teeth that can generallybe characterized as male protrusions and complementary female cavities.

[0052] Referring to FIGS. 10, 13 and 14; bore 7 of clevis 3 may assumevarious orientations in relation to the centerline 22 of clevis 3. FIG.10 depicts bore 7 offset from centerline 22 toward the stop (not shown)of bolt 2. Optionally, bore 7 can be offset from centerline 22 towardthe aperture (not shown) of bolt 2, as shown in FIG. 14, or bore 7 canbe placed in the same plane as centerline 22, as shown in FIG. 13. Itbeing understood that the alternative clevis designs may permit evensmaller total width of connection assembly by bringing the vertebralanchor closer to the rod.

[0053] Details of rod interface washer 4 are shown in FIGS. 18-20. Rodinterface washer 4 can be any of several suitable shapes, including thecircle that is depicted. One surface 23 of the rod interface washer 4has an engagement surface, which preferably includes an engagementgroove 24 that accepts a cylindrical spinal implant rod (such as rod Ain FIGS. 1-3). Engagement groove 24 preferably runs across the entireface of surface 23. Rod interface washer 4 also has a central opening 25that corresponds to the cross-sectional shape of previously presentedwasher seat portion 13 in bolt 2. In the currently preferred embodiment,both washer seat portion 13 and opening 25 are substantially square.Although, this shape could vary from many possible shapes that wouldsimilarly prevent rod interface washer from rotating in respect to bolt2. To assist in this regard, it is also preferable that rod interfacewasher have a guide groove 26 to accept bolt head portion 11 of bolt 2to further lock bolt 2 and rod interface washer 4 together. In thisregard it should be noted that guide groove 26 and engagement groove 24are preferably placed in such a manner that orients aperture 6substantially parallel to groove 24. This placement helps insure that aspinal rod (item A in FIGS. 1-3) will be held in the connector assemblyin a direction that is substantially perpendicular to bolt 2, and inturn, also substantially perpendicular to set screw 5.

[0054] Rod interface washer 4 also includes connection surface 27.Connection surface 27 preferably includes structure for facilitating theengagement of rod interface washer against rotational movement relativeto clevis 3. This engagement structure is preferably a plurality ofvariable angle ridges 28 that radiate from the rotational center of rodengagement washer 4 as that previously described on clevis 3. Variableangle ridges 28 are sized to mate with the similar variable angle ridges21 on clevis 3. Referring to FIGS. 11 and 18, both sets of ridgesconsist of alternating male protrusions and female cavities. Hence, onceplaced together, these interlocking ridges prevent rod engagement washer4 from rotating in respect to clevis 3. And although radiating ridgesare shown to facilitate the fixation of these two parts, it is alsocontemplated that other structures could serve this function. Forexample, it is also contemplated that one could use any number ofinterlocking male and female structures such as rounded bumps orknurling and mating cavities. The locking engagement of connectionsurface 20 with connection surface 27 may occur at any of a plurality ofangles. More specifically, the angle between longitudinal axis LI of thevertebral anchor and longitudinal axis L2 of the rod may be adjusted tomeet the requirements of the patient's anatomy.

[0055] The rotatable connection assembly of this invention is againdepicted in FIGS. 15-17, less set screw 5, which has been removed forclarity along with rod A and vertebral anchor B. The device is used byplacing a spinal rod through aperture 6 in bolt 2. The post of avertebral anchor is then located in bore 7 of clevis 3 and the variableangle ridges 20 on the rod interface washer are interlocked with thevariable angle ridges 28 on clevis 3 as the surgeon desires. Thuslysituated, the assembly is then tightened by threading set screw 5 intoeither of the threaded openings 15 of bolt 2. Upon entering aperture 6,set screw 5 contacts the spinal rod and forces the spinal rod towardinterface washer 4. The spinal rod then contacts rod interface washer 4,and preferably engages groove 24. As one continues turning set screw 5,rod interface washer presses ears 8 and 9 of clevis 3 against stop 10.This action forces ears 8 and 9 together, which in turn, tighten clevis3 around the post of the vertebral anchor. The variable angle surfaces,item 20 on clevis 3 and item 27 on rod interface washer 4, engage eachother and prevent rod interface washer 4 from rotating in relation toclevis 3, which further locks clevis 3 in relation to bolt 2 because rodinterface washer 4 cannot rotate in relation to bolt 2. Adjustments canbe made by loosening set screw 5 then re-tightening the set screw whenthe preferred position has been located.

[0056] Another alternative embodiment of the invention is shown in FIGS.21 to 33. Where possible, like identification numerals have been used toidentify like structures from previous embodiments. Details of bolt 2 inthis embodiment are depicted in FIGS. 24-26, details of clevis 4 aredepicted in FIGS. 27-29, and details of rod interface washer aredepicted in FIGS. 31-33.

[0057] This embodiment is largely the same as the previous embodimentwith two notable exceptions. The first exception is that this embodimentomits end 10. Referring to FIG. 23, bolt 2 (FIG. 24) is still rotablyconnected to eye 17 of ear 9 (FIG. 27). In this embodiment, however,bolt 2 has a threaded portion 70 and ear 9 has a matching set of threads71. When these two structures are operably engaged, bolt 2 is free toturn about its axis just as bolt 2 is free to turn about its axis in theearlier-described embodiments, but end 10 is no longer required. Thesecond exception is depicted in FIG. 30. Bore 7 does not have agenerally round cross-section. Instead, the cross section has beenflattened or raised at two locations 60 and 61. These surfaces forcebolt B against the side of bore 7 at surface 62 when clevis 3 istightened around bolt B, effectively gripping bolt B at three points ofcontact over the length of bolt B. Optionally, one may also wish toprovide a third raised surface at location 62 to contact bolt B.

[0058]FIGS. 34 through 45 depict a connection assembly 101 according toanother embodiment of the present invention. The use of a one-hundredprefix (1XX) before an element number (XX) refers to an element that isthe same as the non-prefixed element number, except for the differencesshown and described.

[0059] This embodiment is similar to the connection assemblies shownpreviously. Connection assembly 101 includes a bolt 102, a clevis 103,and a rod interface washer 104. Bolt 102 includes an aperture 106 forreceiving a rod in a spinal implant system. Clevis 103 includes a bore107 for receiving a vertebral anchor in a spinal implant system.

[0060] Clevis 103 wraps around the shafts of vertebral anchor B and istightened around anchor B when threads 82 of screw 80 are threadablyreceived by internally threaded bore 115 c of bolt 102 (as best shown inFIG. 36). Screw 80 is one example of a separable threaded memberengageable to the threaded end 115 c of bolt 102.

[0061] Screw 80 includes a head 84 having a curved shoulder 86. Shoulder86 is received within at least a portion of pocket 90 defined in outerface 103.3 of ear 109 of clevis 103. Tightening of screw 80 results incurved shoulder 86 bearing against pocket 90. Subsequent tightening ofbolt 80 results in a bending of ears 108 and 109 towards each other,which tightens bore 107 into three point contact with vertebral anchorB. In one embodiment, shoulder 86 is a convex surface having a radius ofabout 0.8 mm. In that same embodiment, pocket 90 is a concave surfacehaving a radius of about 7 mm. However, the present invention is notconstrained to these particular selections of curvature, and alsoencompasses other radii of curvature, as well non-spherical, curvedsurfaces and chamfers. Preferably, the mating surfaces of shoulder 86and pocket 90 are adapted and configured to be in line contact.

[0062] Referring now to FIG. 42, clevis 103 includes a proximal ear 108or end 108 and a distal ear 109 or end 109. Ears 108 and 109 each defineeyes 118 and 117, respectively. Eyes 118 and 117 are preferably circularin cross section and smooth and unthreaded. As can be seen best in FIG.36, the end of bolt 102, which includes internal thread 115 c, passessmoothly through eye 118. The shank of bolt 80 passes smoothly througheye 117.

[0063] Referring again to FIG. 42, ear 108 includes an internal face103.2 that is generally opposite of an internal face 103.1 of ear 109.These opposing internal faces 103.1 and 103.2 are drawn closer to oneanother by tightening of screw 80. Referring to FIG. 42, these opposingfaces are non-parallel to each other when clevis 103 is in a free,unassembled state. In one embodiment of the present invention, theincluded angle E between faces 103.1 and 103.2 is about three degrees,although the invention is not limited to this angle.

[0064] While the invention has been illustrated and described in detail,this is to be considered as illustrative and not restrictive of thepatent rights. The reader should understand that only the preferredembodiments have been presented and all changes and modifications thatcome within the spirit of the invention are included if the followingclaims or the legal equivalent of these claims describes them.

What is claimed is:
 1. A connection assembly between a spinal implantrod and a vertebral anchor, the assembly comprising: a bolt, said bolthaving an aperture for receiving a portion of the spinal implant rod; aone piece clevis, said clevis defining a bore to hold a portion of thevertebral anchor, said clevis having first and second overlapping ears,said ears having substantially aligned channels therein, said boltpositioned within the substantially aligned channels, said first andsecond ears each having an opposing internal face, the opposing facesbeing non-parallel when said clevis is in a free state, one of said earshaving an outer face defining a pocket around the channel; and a screwfor clamping said bolt to said clevis, said screw having a head with acurved shoulder, said shoulder being received within said pocket.
 2. Theconnection assembly of claim 1, wherein said pocket is concave and saidshoulder is convex.
 3. The connection assembly of claim 1, wherein saidpocket has a first radius, said shoulder has a second radius, and thefirst radius is greater than the second radius.
 4. The connectionassembly of claim 1, wherein said clevis engages a non-threaded shaft ofthe vertebral anchor.
 5. The connection assembly of claim 1, whereinsaid pocket is chamfered.
 6. The connection assembly of claim 1, whereinsaid bolt includes a portion with a longitudinal axis, said clevis has asecond channel for receiving said vertebral anchor, and said secondchannel is offset from said longitudinal axis.
 7. The connectionassembly of claim 1, which further comprises a rod interface washerpositioned over a portion of the bolt between the aperture of said boltand an ear of said clevis, said rod interface washer being movable inpart between the aperture of said bolt and said clevis, said rodinterface washer being fixed against rotation relative to said bolt. 8.The connection assembly of claim 1, wherein said clevis has a centerlineand the bore of said clevis is laterally offset from the centerline. 9.The connection assembly of claim 1, wherein said clevis has a centerlineand the bore of said resides in the same plane as the centerline. 10.The connection assembly of claim 1, wherein said channels in said clevisare holes.
 11. The connection assembly of claim 1, wherein the bore insaid clevis is adapted and configured to engage a vertebral anchor atthree points of contact.
 12. The connection assembly of claim 11,wherein said pocket is concave and said shoulder is convex.
 14. Theconnection assembly of claim 12, wherein said bolt includes a portionwith a longitudinal axis, said clevis has a second channel for receivingsaid vertebral anchor, and said second channel is offset from saidlongitudinal axis.
 14. A connection assembly between a spinal implantrod and a vertebral anchor, the assembly comprising: a bolt, said bolthaving an aperture for receiving a portion of the spinal implant rod,said bolt having a threaded end; a clevis, said clevis defining a boreto hold a portion of the vertebral anchor, said clevis having first andsecond overlapping ears, said ears having substantially aligned channelstherein, the threaded end of said bolt being positioned within thesubstantially aligned channels; and a separable threaded memberthreadably engaged to the threaded end of said bolt.
 15. The connectionassembly of claim 14, wherein said separable threaded member is a screwhaving external threads engageable with internal threads of said bolt.16. The connection assembly of claim 14, wherein tightening of saidseparable threaded member and said bolt clamps together said first andsecond ears.
 17. The connection assembly of claim 14, wherein one ofsaid ears has an outer face defining a pocket around the correspondingchannel, and said separable member includes a curved shoulder receivedwithin said pocket.
 18. The connection assembly of claim 17, whereinsaid pocket is concave and said shoulder is convex.
 19. The connectionassembly of claim 18 wherein said pocket has a first radius, saidshoulder has a second radius, and the first radius is greater than thesecond radius.
 20. The connection assembly of claim 14, wherein saidclevis engages a non-threaded shaft of said vertebral anchor.
 21. Theconnection assembly of claim 20, wherein said bolt includes a portionwith a longitudinal axis, said clevis has a second channel for engagingsaid vertebral anchor, and said second channel is offset from saidlongitudinal axis.
 22. The connection assembly of claim 14, whichfurther comprises a rod interface washer positioned over a portion ofthe bolt between the aperture of said bolt and an ear of said clevis,said rod interface washer being movable in part between the aperture ofsaid bolt and said clevis, said rod interface washer being fixed againstrotation relative to said bolt.
 23. The connection assembly of claim 22,wherein said clevis has a centerline and the bore of said clevis islaterally offset from the centerline.
 24. The connection assembly ofclaim 23, wherein the bore in said clevis is adapted and configured toengage a vertebral anchor at three points of contact.